With rapid development in communication systems, MC (Multi-Carrier) technology has drawn great interests from the industry and the academia due to its advantages in anti-interference, parallel transmission, resource allocation optimization and etc.
On the one hand, a broadband system may distribute a signal over multiple carriers by using MC technology, adopts data interleaving and carrier interleaving, to mitigate frequency-selective fading.
On the other hand, there is generally more downlink traffic than uplink traffic in a wireless communication system. Typically, for a downlink transmission, a transmitter may establish information association between multiple carriers by using carrier interleaving, FEC (Forward Error Correction) or the like. The receiver may recover information lost during the transmission by using the information association. Furthermore, the downlink traffic is usually distributed across a broader frequency band and thus has a stronger capability for mitigating frequency-selective fading. In contrast, for an uplink transmission, it's very difficult to coordinate multiple users to establish information association with techniques such as carrier interleaving, and each user's uplink traffic only occupies a narrower bandwidth. Accordingly, the uplink traffic is more vulnerable to frequency-selective fading.
Typically, a sub-carrier may show different channel characteristics for different terminals as the space and the time vary. Due to the difference in spatial characteristics, such as propagation paths, barriers and so on, a sub-carrier may show frequency-selective fading for a set of terminals and good channel characteristics for another set of terminals at a certain time. Additionally, a sub-carrier may alternate, with time aging, between a poor channel subjected to frequency-selective fading and a good channel suitable for transmission as the same terminal is concerned. Therefore, it will be a method for enhancing system performance to allocate different sub-carriers to different terminals in a multi-carrier system based on the fact that different sub-carriers demonstrate different channel characteristics for different terminals.
A method for performing transmissions between a plurality of mobile terminals and a base station over a plurality of sub-carriers is described in a U.S. patent application with No. 20050249127 A1 published on Nov. 10, 2005, filed by Lucent Technologies Inc. In this method, the channel quality of at least a portion of sub-carriers for each mobile terminal is estimated and a respective set of sub-carriers is selected for each mobile terminal based on the estimation and the allocation is informed to each mobile terminal; and each mobile terminal performs transmission over its allocated set of sub-carriers.
It is, therefore, necessary to provide a method for optimization of carrier allocation and improvement of system performance in a TDM multi-carrier system.